Even if these ionizing radiations are different, they have the same chemical and biological effects. None of these radiations has sufficient energy to induce radioactivity. Whether every mass element of a food requires irradiation will depend on the purpose of the treatment. In some cases, irradiation of the surface will suffice. In other cases, the entire food must receive at least the minimum dose. Because irradiation causes practically no temperature rise in the food processed, it is in effect a non-thermal technology that may even inactivate microorganisms in frozen food without thawing it. An effective radiation dose can be delivered through most standard food-packaging materials, including those that cannot withstand heat. This means that irradiation can be applied to hermetically sealed products without the risk of recontamination or reinfestation of properly packaged foods. Some food products may have to be irradiated under special conditions, for example, at low temperature or in an oxygen-free atmosphere. Others may undergo a combination treatment, using, for example, both radiation and heat. Processing by irradiation, either alone or in combination with other treatments, offers some advantages over conventional methods of food processing.